Rats and other rodents often find their way into residential houses and other properties via sewage pipes. This is undesirable, since rodents can cause many problems from a sanitary, health-related and safety-related aspect. If rodents are able to move freely in the sewage system, they can make their way up through floor drains and also toilets. Since most sewage pipes in modern buildings are made of plastic material, there is also an obvious risk of rodents gnawing through the sewage pipes so that these begin to leak, or, if they run through earth, even fill with earth and other filling material, which leads to blockages in the sewage system. Furthermore, rodents act as spreaders of disease in properties and can sometimes even cause fires by gnawing through electric cables. For these reasons, various attempts have been made to prevent rodents from getting into houses and other properties via sewage pipes.
A mechanical solution to the problem in question is presented in WO 03/069082. The arrangement described in the document is based on the use of two tiltable, oblique shutters in a horizontal part of the sewage system. When a rodent moves against the stream up through the sewage pipe and reaches the first shutter and actuates this, the second shutter is allowed to tilt to a limited extent such that the sewage water flow is some-what restricted and acquires higher flow velocity, whereupon the rodent is incapable of withstanding the stream of water.
The arrangement is dependent, however, upon a good and lasting functioning of the mechanical parts and also upon a high flow in the sewage system. Furthermore, the arrangement can only be used in horizontal or approximately horizontal parts of the sewage system.
The arrangement described in WO 2006/053562, which is based on two mechanically interacting shutters, is also subject to the same draw-backs as the abovementioned arrangement.
A further mechanical solution is shown in U.S. Pat. No. 5,090,152 and corresponding Swedish published patent application 8801346-1. The arrangement described in the document is intended to be placed in a vertical part of the sewage system and is formed by a ring of rods, which converge in the direction of flow in such a way that the rods prevent the rodents from passing upwards past the rod ring, but which rods bend outwards to let past solid material which may accompany the sewage water.
An arrangement of this latter type cannot be used, however, in horizontal pipes or ducts.
Based on the above, there is therefore a need for an arrangement which prevents the advance of vermin in pipes and which overcomes the aforementioned obstacles.